How does shutting the product down get them any customers?

"Hey you've been paying for this calendar thing for a while, but won't be able to any longer. Go use one of their competitors instead. BTW have you tried our CRM?"

Because you might shift them to another product line?

I don't personally care about Salesforce and think they're a low/mediocre company, but having seen acquisitions at my last company we'd shut them down but roll them into our ecosystem.

Obviously there's churn, but that's why you spend MONTHS doing due diligence to figure out if the strategy is sound. For example, most of the customers of one product we acquired were already using our product for other things, or competitor platforms. So, we managed to roll a bunch of enterprise customers onto our platform.

Its not just LOOK AT ME I WROTE SOME CODE :D lol

Or they might just be buying out the team to help them build out something to address gaps in their product.

But it is not just "why can't they just make it themselves"

To be fair, Salesforce IS a CRM and can offer people project/time/calendar/team collaboration features, even if it's not a DIRECT competitor to a modern wave of time management startups.